\(V\)  is the Cabibbo–Kobayashi–Maskawa (CKM) mixing matrix for
quarks [1]}, [2]}. As a result of the fact
that \(V\)  is not diagonal, the \(W^\pm \)  gauge bosons couple to quark
mass eigenstates of different generations. Within the Standard
Model, this is the only source of flavour-changing quark
interactions.
